U.S. Pat. Nos. 7,134,279 and 7,171,811 disclose Multiple cylinder, free piston Stirling engines. By a free piston machine or engine is meant a machine or engine which does not use a kinematic mechanism to mechanically link the pistons together and to a rotating shaft. Instead, in the case of an engine power is absorbed using linear electric generators driven one by each piston. The electrical outputs of the generators may be combined. In the case of a machine in which the pistons are driven such as a pump or a compressor, each piston is driven independently, by a linear electric motor for example.